The Bill makes a substantial concession to farmers by treating agricultural (not fossil) methane differently from the longer-lived gases. Some environmentalists have focussed their outrage on this but there is some scientific basis for it. While carbon dioxide breaks down very slowly and most of it lasts in the atmosphere for thousands of years, methane reduces to half in about 12 years, and tails off slowly after that. However the heat it produces does not decay, so it still has an effect. The key question is: if not to zero, how far should methane be reduced to stabilise the climate?

Some farmers are saying we should just stabilise it at today’s levels or a little less. That won’t do: it has risen some 6% since the 1990 baseline established at Kyoto and that has produced substantial extra warming we now have to take out of the atmosphere.

A majority of submissions on the discussion paper last year demanded that methane emissions should go to zero by 2050. It seems unreasonable to imagine that not a single cow or sheep would remain in NZ after that date; pre-agriculture, there were substantial herds of wild ruminants (though not in NZ, and vastly less than current domestic cattle) and the climate was more or less in balance then.

The Bill requires a 10% reduction in methane by 2030 and 24-47% by 2050. Farmers, in campaigning mode, have focussed their outrage on the 47%. However the important one is the 10% by 2030, not the 20-47% by 2050.

What we do in the next ten years matters most. Science, public opinion, and politics are changing rapidly (think how much has changed in the last 2 years). Any target beyond that is likely to be changed anyway, and it will be getting too late to matter unless we have taken earlier action.

When methane is first released it produces a very powerful spike of warming. Over twenty years (rather than the 100 year that has become the international metric) it is 86 times more powerful than carbon dioxide (IPCC 2013). Cutting methane now is the fastest action we could take to slow the rate of warming. Whether it is cut all the way to zero is much less important.

And the point is, it’s not hard, some farmers are already doing it, and it increases farm profits.

Most people are still refusing to recognise that a 20% cut in dairy cow numbers increases farmers’ profits. This is because the associated drop in urea and bought in feeds reduces input costs, and there is an increase in milk production per cow when fed the extra grass that 20% would have eaten.

It gets better. Fewer cows, fed better, healthier and less stressed reduces nitrous oxide emissions and nitrogen runoff to rivers. Why would we regard just half that free gain as a stretch goal in 11 years’ time? It’s nonsense, from a farmer’s point of view. They could do it in a couple of seasons without culling more cows; most dairy cows are only kept for about 7 years, then sent to the works. If we started keeping fewer dairy heifers each year from now on we could reduce herd numbers by 20% in less than 5 years.

The evidence for it has been around for about 5 years, including Alison Dewes, Peter Fraser (the “marginal cow”), Barry Ridler, and modeling done at Massey university (Sulzberger et al) all with impeccable credentials. If we could get this more widely known, people would ridicule farmers for ignoring their own self interest.

Never mind the reductions after this. If farmers reduced methane 20% by 2025, reducing cow numbers, reducing input costs and increasing production per cow, they would get public support, buy themselves some time and make more money! Once on this trajectory 24% by 2050 will be obviously pathetic and 50% well within reach.

The key is to waste no more time. The earlier the emissions cuts, the more valuable they are.